A popular interface for computers is the SCSI standard interface. Peripherals such as hard disk drives and CD ROMS made by some manufacturers meet the SCSI standard, but some do not. The SCSI standard dictates the use of an SCSI interface circuit board plugged into a slot of the computer, and a standard socket that is externally available into which a plug wired to a peripheral (device) may be connected. Pins of the SCSI socket connect to predefined and standard signal lines.
However, some manufacturers make peripherals that are proprietary, and do not meet the SCSI standard. If the computer owner wishes to use different peripherals at different times, or wishes to change peripherals, a different interface circuit board must be purchased with a circuit and socket that matches that of the different peripheral, and plugged into the computer, with the attendant requirement to remove the cover of the computer and risk damage to the computer, or at least disruption to the physical environment of the user as well as to work that must be done using the computer. For proprietary CD ROMs, for example, a unique interface circuit and a different connector is required for each type of CD ROM. This precludes a design that supports multiple types of CD ROMs without many circuit boards and connectors and which use up valuable empty slots of the computer motherboard.